ML19345G113
| ML19345G113 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 11/27/1974 |
| From: | Searls F, Searls J PACIFIC GAS & ELECTRIC CO. |
| To: | Goller K US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| 12145, RO-DPR-7-74-7, NUDOCS 8103020471 | |
| Download: ML19345G113 (3) | |
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PACIFIC GAS AND E LE C T RI C C O M PANY EOWE:e l
77 BEALE STREET. S A N F R AN CISCO, C ALIFO R NI A 94106.(415) 781-4211 meesaru.
P R E D E R I C K T. S E A R L S November 27, 1974 E!!Kii;ES-
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JOHN C. MOR RISSEY
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Mr. Karl R. Gollcr
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Office of Regulation
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U. S. Atomic Energy Commission yS 1-2 Washington, D. C. 20545 i_-
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Docket No. 50-133 y
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Humboldt Bay Power Plant C-
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Caar Mr. Goller:
This report is submitted in accordance with the require-ments of Section IX.H.2.a. (4) of the Technical Specifications of License No. DPR-7.
Notification of the occurrence covered by this report was made via telephone to the Director of Region V Regulatory Operations within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of the occurrence.
1 Report Number DPR-7/74--4 Report Date November 27, 1974 Occurrence Date November 17, 1974 Facility Humboldt Bay Power Plant, Unit No. 3, Eureka, California Identification of Occurrence:
Five of the eight feedwater sparger hold-down U-bolts failed allowing the sparger to shift approximately 1.7 inches from its initial l
location.
l Description of Occurrence:
On October 30, 1974 the reactor was shutdown for a regularly scheduled refueling outage.
On November 17, 1974 during a routine reactor vessel visual inspection it was discovered that five of the l
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Mr. Karl R. Goller 2
November 27, 1974 eight feedwater sparger hold-down U-bolts had failed where the bolt enters the upper lock nut.
Three of the bolts had both legs broken, the other two had only one leg broken.
Measurements taken on Novem-ber 19, 1974 indicated tha'c the sparger and thermal sleeve had shifted approximately 1.7 inches away from the vessel inlet nozzle.
With this movement, the sparger thermal sleeve still extends approximately 22.6 inches into the nozzle.
Designation of Apparent Cause:
It is thought that the heatup and cooldown cycle normally experienced during plant operation or hydraulic forces caused the t
sparger to creep away from the feedwater inlet nozzle, eventually exerting sufficient shearing force on the U-bolts to break them.
Two of the broken bolts are being tested to attempt to identify the failure mechanism.
Analysis of Occurrence:
The failure of the bolts and movement of the sparger did not impair the ability of the sparger to perform its intended function during i
either normal or accident conditions.
During the last operating cycle there were no indications that there was any change in the thermal hydraulic operating characteristics of the feedwater or reactor systems due to this failure.
Since the thermal sleeve is an interference fit I
and the nozzle I.D. is uniform for the entire length of the nozzle, I
there would be no increase in feedwater flow around the sleeve as a l
result of the shift in the sparger.
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Corrective Action:
I Work is currently in progress to return the sparger to its original location and install re-designed hold-down clamps to replace the broken U-bolts.
This work is being conducted utilizing the original vendor as a consultant.
A thorough inspection of the sparger and hold-down clamps will be made during future regularly scheduled refueling l
outages to assure that the new clamps are performing satisfactorily.
Failure Data:
There have been no previous failures of this type observed.
The feedwater sparger and U-bolts were manufactured by Combustion Engineering, Inc., Chattanooga, Tennessee for General Electric Company as an integral part of the reactor vessel.
Should further assessment of this event indicate increased
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Mr. Karl R. Goller 3
November 27, 1974 1
significance or changes.in the findings reported, a corrected report will be submitted as expeditiously as possible.
Very truly yours, s
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Mr. R. H. Engelken, Director Directorate of Regulatory Operations Region V I
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